1. Field of the Invention
This invention relates to a nonreciprocal circuit device such as an isolator, etc., used in a high-frequency bandwidth of a microwave band, etc., and a communication device using the device.
2. Description of the Related Art
Up to now, a lumped-constant-type circulator is constructed in such a way that a plurality of central conductors intersecting each other which are disposed in the vicinity of a ferrite plate and a magnet for applying a direct-current magnetic field to the ferrite plate are housed inside a case. Moreover, an isolator is constructed by connecting a fixed port out of three input/output ports in a circulator to a terminating resistor.
FIG. 12 is an exploded perspective view of a conventional isolator. Here, a box-shaped upper yoke 2 of a magnetic metal and a disk-shaped permanent magnet 3 disposed on the inner surface of the upper yoke 2 are shown. Moreover, an assembled magnetic body 5 is constructed in such a way that a disk-shaped ferrite 54 is placed in the joining portion of central conductors in the same shape as the bottom face of the ferrite 54, three central conductors extending from the above joining portion are bent and disposed so as to wrap the ferrite 54 with an angle of nearly 120 degrees to each other, and the input/output ports P1, P2, and P3 at respective ends of each of the central conductors are made to protrude outwards. Matching chip capacitors C1, C2, and C3 are connected between the input/output ports P1, P2, and P3 and a grounding electrode inside a resin case 7. A terminating chip resistor R is connected between an electrode conductive to the input/output port P3 and the grounding electrode. The resin case 7 is shown. A lower yoke 8a of a magnetic metal combined together with the upper yoke 2 constitutes a closed magnetic circuit. Several elements and parts in FIGS. 12-13B correspond to elements and parts described in connection with the first embodiment (FIGS. 1-4) and duplicative descriptions of those elements and parts are omitted.
FIG. 13A is a sectional view of a main part of the conventional isolator shown in FIG. 12. One terminal electrode of the chip resistor R is connected to the grounding terminal 73. To the other terminal electrode of this chip resistor R, the input/output port P3 is soldered. Moreover, the chip capacitor C3 is connected between the input/output port P3 and the grounding terminal 73.
In such a construction in which the terminal electrode of the chip resistor R used as a terminating resistor is insulated from a metal case 8 by the bottom portion 7b of the resin case, the bottom portion 7b of the resin case is required to be made 0.2 mm or more in thickness in order to ensure the fluidity of resin inside the molding die when injection molding is performed by using resin, and the condition is unfavorable for low-profile products to that extent.
Then, as shown in FIG. 13B, a construction in which the terminal electrode, that is, the portion to which the input/output port P3 of a center electrode is connected, of the chip resistor R is provided only on the opposite side to the metal case 8 and the other terminal electrode of the chip resistor R is directly soldered to the metal case, can be also adopted. Furthermore, as shown in FIG. 13C, also lower-profile products can be obtained by soldering the chip capacitor C3 directly to the metal case 8.
However, in such a construction in which the chip components are directly soldered to the metal case 8, when the soldering pasts coated on the terminal electrodes, etc., is melted, the melted solder is confined in a narrow space between the terminal electrode to which the input/output port of a center electrode is connected and the metal case 8, and then cases in which a ball-shaped solder B remains as shown in the drawings sometimes occur. If such a ball is caused, it is feared that the above terminal electrode and the metal case 8 may be short-circuited and that the electrode on the hot side of the chip capacitor C3 and the metal case may be short-circuited.
It is an object of the present invention to provide a nonreciprocal circuit device which may be made low-profile and in which short-circuiting by a solder ball can be prevented and a communication device using the device.
In the present invention, a nonreciprocal circuit device comprises a magnetic body to which a direct-current magnetic field is applied, a plurality of central conductors which are coupled in a different direction to the magnetic body with each other, and chip components connected between the input/output port of each of the central conductors and a metal case, wherein a hole is formed in the metal case at a position which is located in the proximity of the terminals of the chip component to which the input/output ports are connected. Because of such a configuration, the connection portion of the input/output port of the chip component is made open by the hole and the possibility of a solder ball remaining therein is made very rare, and thus the occurrence of a defect such that the terminal electrode of the chip component or the input/output port of a central conductor is short-circuited to the metal case via solder ball is prevented.
Moreover, in the present invention, an insulating material is filled or inserted in the hole. In this way, the terminal portion of a chip component is prevented from loosening in the hole portion and the whole bottom portion of the chip component is made in contact with the insulating material filled in the hole and the metal case to stabilize the chip component. Moreover, the inside of the metal case is sealed to improve the reliability of the nonreciprocal circuit device.
Moreover, in the present invention, the above insulating material constitutes a part of a resin case containing the chip components, etc. In this way, the total number of parts is reduced and cost reduction is achieved.
Moreover, in the present invention, the opening in the external surface of the metal case is narrower than the opening in the inner surface thereof. Because of such a construction, a space which is to be insulated from the metal case and which is located in the vicinity of the terminal electrode of a chip component is widened. The opening area toward the outside of the metal case is reduced, and accordingly the environmental resistance is enhanced.
Moreover, in the present invention, the chip component has a substantially parallelepiped shape, terminal electrodes are formed on opposing sides in the longitudinal direction or the transversal direction of the chip component, one terminal electrode is connected to the metal case and the other terminal electrode is formed only on the opposite side to the metal case. According to this construction, a distance between the terminal electrode on the hot side and the metal case is increased, the terminal electrode on the hot side is the terminal electrode of a chip component which is located opposite to the side to be connected to the metal case. Accordingly the possibility of short-circuiting is more surely avoided and the reliability can be further increased.
Furthermore, in the present invention, a communication device is constructed by using a nonreciprocal circuit device having any of the above construction.